S1 [LEC]: RENAL FUNCTION Flashcards
Four main components for the excretion of unwanted substances
Kidney
Ureters
Bladder
Urethra
Connects the urinary system with reproductive system
Urethra
Allows gas exchange
Capillaries
Renal Function:
Allow substances to be removed or filtered
Glomerular Filtration
The functional unit of the kidney
Nephron
Approximate number of nephrons per kidney
1-1.5 million
Nephron responsible for the removal of waste products and reabsorption of nutrients
Cortical (85%)
Nephron responsible in the concentration of urine and reabsorption of water
Juxtamedullary (15%)
Human kidney receives ___ of the blood
25%
Blood enters the nephron via ___
afferent arteriole
Blood flows through the glomerulus and into the ___
efferent arteriole
Blood from the efferent arteriole enters the ___ and ___ for immediate reabsorption
Peritubular capillaries
Vasa recta
Provides for immediate reabsorption of essential substances for proximal convoluted tubule and distal convoluted tubule
Peritubular capillaries
Normal value of total renal plasma flow
600-700 mL/min
Normal value of total renal blood flow
approx. 1200 mL/min
Nonselective filter of plasma substances
Glomerulus
Plasma filtrate must pass through three membranes, namely:
- Capillary wall membrane
- Basement membrane (basal lamina)
- Visceral epithelium of the Bowman’s capsule
Results from the smaller size of the efferent arterioles and the glomerular capillaries
Glomerular Pressure
T/F: Glomerular pressure enhances the filtration process
True
Regulates the blood flow to and within the glomerulus
Renin-Angiotensin-Aldosterone System (RAAS)
RAAS respond to changes in the ___ and ___
Blood pressure
Plasma sodium content
Responsible for vasoconstriction
Angiotensin II
Responsible for sodium reabsorption
Angiotensin II (PCT)
Aldosterone (DCT)
Responsible for water reabsorption
ADH
Plasma concentration where the active transport stops
Renal threshold
Reabsorption of water happens in the renal tubules except in ___
Ascending loop of Henle
Renal threshold of glucose
160-180 mg/dL
Identify the cellular mechanism of reabsorption:
Glucose, amino acids, salts
Active
Identify the cellular mechanism of reabsorption:
Chloride
Active
Identify the cellular mechanism of reabsorption:
Sodium
Active and Passive
Identify the cellular mechanism of reabsorption:
Water
Passive
Identify the cellular mechanism of reabsorption:
Urea
Passive
Renal concentration begins in the ___
Descending and ascending loop of Henle
Na and Cl are reabsorbed in the ___
Ascending loop of Henle
Water is removed by osmosis in the ___
Descending loop of Henle
Ensures the unidirectional flow of urine
Countercurrent mechanism
A selective reabsorption process that serves to maintain the osmotic gradient of the medulla
Countercurrent mechanism
Involves the passage of substances from the blood in the peritubular capillaries to the tubular filtrate
Tubular secretion
Two major functions of tubular secretion
- Elimination of waste products not filtered by glomerulus
- Regulation of acid-base balance through secretion of H ions
How many percent of bicarbonate should be reabsorbed to ensure it buffering efficiency in the blood?
100%
Major site for removal of nonfiltered substances
Proximal convoluted tubule
Measures the rate in mL per minute at which the kidneys are able to remove a filterable substance from the blood
Glomerular filtration test
An exogenous substance that is a polymer of fructose and is used in clearance test in the past
Inulin
A clearance test used in the past which requires a 2-hour sample
Urea clearance test
Most commonly used clearance test
Creatinine clearance test
The earliest clearance test
Urea clearance test
The main advantage of inulin clearance test
Extremely stable, not reabsorbed
Used for routinely screening patients as part of a metabolic profile and to monitor patients already diagnosed with renal disease or at risk for renal disease
eGFR
A clearance test recommended for pediatric patients, elder, people with diabetes, and critically-ill patients
Cystatin C clearance test
Dissociates from human leukocyte antigen at a constant rate and is removed rapidly from the plasma by glomerular filtration
Beta 2-microglobulin (B2M)
Most sensitive indicator of a decrease in GFR
Beta 2-microglobulin (B2M)
Used to determine the ability of the tubules to reabsorb essential salts and water that have been non-selectively filtered by the glomerulus
Concentration test
Measures only the number of particles in a solution
Osmolality
Performed for a more accurate evaluation of renal concentrating ability
Osmolality
Determines the ability of the kidney to respond to the body’s state of hydration
Free water clearance
Most commonly associated test with the tubular secretion and renal blood flow
P-aminohippuric acid (PAH)
Standard tests used to measure the filtering capacity of the
glomeruli
Clearance tests
Tests to determine the ability of the tubules to reabsorb the essential salts and water that have been nonselectively filtered by the glomerulus
Concentration tests
Repels small molecules with a negative charge
Shield of negativity
A restriction for large molecules that is present in the basement membrane and thin membranes covering the filtration slits
Podocytes
T/F: Pores increase capillary permeability but do not allow passage of large molecules and blood cells
True
T/F: Glomerular pressure enhances water reabsorption
False (it enhances filtration)
The angiotensin converting enzymes are produced in the ___
Lungs
The ADH is stored in the ___
Posterior pituitary gland
Where are Glucose, Amino acids, Salts reabsorbed?
PCT
Where is Chloride reabsorbed?
Ascending Loop of Henle
Where is sodium reabsorbed through active transport?
PCT & DCT
Where is water reabsorbed?
PCT, Descending Loop of Henle, Collecting Duct
Where is urea reabsorbed?
PCT, Ascending Loop of Henle
Where is sodium reabsorbed through passive transport?
Ascending Loop of Henle
Sample required in urea clearance test
2-hour urine sample
Reference range of creatinine clearance in males
107-139 mL/min
Reference range of creatinine clearance in females
87-107 mL/min
Normal plasma creatinine level
0.6-1.2 mg/dL
Most frequently used formula for eGFR
Modification of Diet in Renal Disease (MDRD) – Isotope Dilution Mass Spectrophotometry (IDMS)
An obsolete test that compares the volume and specific gravity of the urine sample during day and night to evaluate concentrating ability
Mosenthal test
An obsolete test wherein the patient is deprived of fluids for 24 hours before the specific gravity of the urine is measured
Fishberg test
A test for unilateral kidney function
Indigo Carmine Test
What oral acid load is used for Titratable Acidity and Urinary Ammonia?
Ammonium chloride
Reference range for Titratable Acidity and Urinary Ammonia
70 mEq/day of acid in the form of titratable H or NH4
Factor for eGFR if the patient is female
0.742
Factor for eGFR if the patient is black
1.212
One of the advantages of this test is that it is independent of muscle mass
Cystatin C clearance test
The varying sizes of the arterioles help to create the ___ important for glomerular filtration
Hydrostatic pressure
The exchange of water and salts maintains ___ in the medulla
Osmotic gradient
The glomerular filtration barrier is located within what structure?
Bowman’s capsule
An increase in blood pressure results in ___ of the afferent arterioles to prevent overfiltration or damage to the glomerulus
Constriction
An enzyme secreted by the juxtaglomerular cells that reacts to produce angiotensin I
Renin
As angiotensin I passes through the alveoli of the lungs, ___ changes it to the active form angiotensin II
Angiotensin-converting enzyme (ACE)
Enzyme that corrects renal blood flow through vasodilation of afferent arterials and triggering aldosterone
Angiotensin II
Reabsorption depends on the osmotic gradient in the medulla and which hormone?
Vasopressin (ADH)
Where major exchanges of water and salts take place between blood and medullary insterstitium
Vasa recta
